/**
 * Реализация hook_menu()
 */
function mymodule_menu() {
  $items['export'] = array(
    'title' => 'Export',
    'page callback' => 'drupal_get_form',
    'page arguments' => array('mymodule_export_form'),
    'access arguments' => array('administer site configuration'),
  );
  return $items;
}
 
/**
 * Форма экспорта
 */
function mymodule_export_form() {
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Экспорт',
  );
  return $form;
}
 
/**
 * Экспорт
 */
function mymodule_export_form_submit($form, &$form_state) {
  $data = 'Hello World!';
  header('Content-Disposition: attachment; filename=somename.txt');
  header('Content-Type: text/plain; charset=utf-8');
  echo $data;
  exit;
}